Thread-cutting die



Now-2; 1943.

M. L. BURT THREAD CUTTING DIE Filed Jill 25, 1942 lOCb f I08 653a,

' Figure 2; and

Patented Nov. 2, 1943 UNITED STATES PATENT OFFICE 1111;133:333: ii g lzi iv fij;,110

8'Claims. (61.10-116) This invention relates to iniprovements in thread cutting tools and adjustable hollow mill for cutting and removed from the tool and sharpened individually.

Usually with tools made for cutting accurate threads onstock of rather small diameter, where the threads made must be of uniform pitch dimension and very accurately cut, the cutters are formed as integral sections of a block. With such construction it is very diilicult to sharpen the cutter sections when they become dull. It is sometimes impossible to get a stone or wheel between them and even when possible it is still more diflicult to sharpen all the sections alike so that each-will bear its proportionate part of the cutting operation.

The primary object of my improvements is to provide separate and distinct cutters which may be easily removed from the tool and individually sharpened. Thisnot only makes the task' of sharpening-much easier and quicker to perform but enables all the cutters to be sharpened alike. Another object of the improvements is to provide simple means for accurately positioning and holding the separate cutters in place on the tool and in providing for their close adjustments to insure that the desired threads may be produced with the requisite accuracy.

The best mode in which I have contemplated applying the principles of my improvements is shown in the accompanying drawing but these are to be deemed illustrative because it is intended that the patent shall cover by suitable expression in the appended claims whatever features of patentable novelty exist in the invention disclosed.

- In the drawing:

Figure 1 is an exploded view of the several parts of my improved tool in separated relations;

Figure 2 is a longitudinal section, taken as on line 22 of Figure 3, of the assembled tool;

Figure 3 is a section taken as on line 3-3 of Figure 4 is a perspective of one ofthe cutters. Referring to the drawing, and particularly to Fig. 1, the tool comprises a body It, a pilot bushing I2, positioning pins I4, a series of separate individual cutters IS, a locking nut I8, and an adjusting nut'lll.

The body has a suitable shank Illa, either of 'a releasing or non-releasing type, the latter being shown in the drawing. Near one end the body has an enlarged cylindrical section Iflb which is externally threaded, and beyond these threads there is a cylindrical surface Illc. At its cutter-- holding end tha body is accurately faced at IIId perpendicularly to its axis. hole Ifle in the face of the body receives the shank In of the pilot bushing which has a cir- 'cularly flanged head I2b whose external cylindrical surface I2c determines primarily the diametrical dimensions of the threads to be cut. Pilot bushings having shanks of common size but heads of different diameters can be inserted in the body to enable the back diameter of a set of cutters to be very slightly increased and thereby prevent the cutting of any tapered portions of a thread.

Secured in the face end of the body are two or more positioning pins I4 which serve to space the cutters I6 circumferentially. An axial hole is provided through the shanks and bushing to allow cutting oil'to be forced to the cutting edges of the cutters.

There may be two or more cutters, four are shown, each of which is made identical with the others. Each cutter has a shank I6a which is a portion of a cylindrical wall having at its base or body end an outstanding bev'eled surface I6b. As seen best in Fig. 3, the body end of the cutter has sides IIic cut on radial planes from the tool axis and normally these sides rest against the positioning pins I4. This is not essential, however, and indeed if a larger pilot bushing is used,- thus positioning the cutters slightly farther away from the tool axis, the radial sides of the cutters can not be in contact with two pins at the same;

' its cutting end the cutter body extends inwardly to provide a round beveled external surface id and to bring the cutting teeth I6e well in toward the tool axis. The teeth are very accurately formed with the usual relief toward one side.

The cutters are secured to the body by the nut I8 which at one end has internal threads which screw onto the external threads of the enlarged cylindrical section Illb of the tool body. Although not shown in the drawing, it is to be understood that a lock nut may also be screwed onto these same external threads to lock the cutter holding nut I8 in place. this latter nut has external threads I8a to receive the adjusting nut 20. "Interiorly the cutter holding nut has a cylindrical surface I lb somewhat greater in diameter than is the cylindrical A carefully formed The other end of surface I of the body. Beyond, in direction toward the cutting end of the tool the cutter holding nut has a beveled surface l8c which engages the corresponding beveled surfaces lib on the shank ends of the several cutters. As the nut I8 is tightened, the engagement of these: beveled surfaces seats the cuttersagainst the cylindrical surface We of the head of the pilot bushing and also against the face IOdof the body. Thus the cutters are firmly and accurately secured in posi ion.

The adjusting nut 20 has internal threads which screw onto the external threads l8a of the cutter holding nut and has a cylindrical skirt 20a terminating in a circular flange 20b which extends inward. This flange has a beveled inner edge or surface 200 which corre-. sponds to the external beveled surfaces Hid on the cutting end of the cutters. Accordingly, when the adjusting nut is tightened to bring its beveled surface against the cutters the latter are reinforced against any tendency to spring outward. And by tightening the adjusting nut still further, the cutting ends of the cutters may be sprung inwardly slightly to obtain an exceedingly fine adjustment.

I claim:

l. A thread cutting die comprising a cylindrical body having external threads, a fiat face at one end perpendicular to the axis of the body and an axial hole; a pilot bushing having a shank fitting within said axial hole and a flanged cylindrical head overlying a portion of said flat face; positioning pins mounted in said body and outstanding from said flat face outside the bushing head; a series of cutters each having a base portion with a fiat end surface, a flat radial surface, an internal cylindrical surface and an external beveled surface and having a forwardly extended cutting portion with internal cutting teeth and an external beveled surface; a clamping nut having internal threads to engage the external threads on said cylindrical body, an internal beveled surface to engage the beveled surface on the base portion of each cutter, and having external threads; and an adjusting nut having internal threads to engage the external having external threads therearound, a fiat faced end, and an axial hole; a pilot bushing in said hole having a'cylindrical head overlying a portion of said flat faced end; a series of cutters each having a fiat faced end, an internal cylindrical surface, and an external beveled surface;

a clamping nut threadable on the external threadsof said body and having an internal beveled surface engaging the external beveled surface of each cutter, whereby upon the nut being tightenedo'n said body the flat faced ends of the cutters are seated against the flat faced end of the body and the internal cylindrical surfaces of the cutters are seated against the cylindrical head of the bushing.

3. A thread cutting die comprising a body having a flat faced end and an axial hole; a pilot bushing in said hole having a head overlying a portion of said fiat faced end; a series of cutters each having a flat end face, an internal surface, and an external beveled surface and a clamping element adapted to be secured to said body having an internal beveled surface engaging the beveled surface of each cutter whereby the flat end face of the cutter is held against 'the flat faced end of the body and the external surface of the cutter is held. against the head of said bushing.

4. A thread cutting die comprising a body having a fiat facedend and an axial hole; a pilot bushing in said hole having a head overlying aportion of said flat faced end; a series of cutters each having a flat end face, an internal surface, and spacedapart external beveled surfaces; a clamping element adapted to be secured to said body having an internal beveled surface engaging one of the beveled surfaces of each cutter whereby the flat end face of the cutter is held against the flat faced end of the body and the internal surface of the cutter is held against the head of said bushing; and an adjusting element adapted to be secured to said the body and the said bushing; and an adjusting element adapted to be secured to said clamping element having an internal beveled surface engaging the other beveled surface of each cutter whereby the cutters may beadjusted simultaneously.

6. A thread cutting die comprising a cylindrical body having a. fiat face perpendicular to its axis; a pilot bushing associated with said body having a cylindrical edge outstanding from said fiat face; positioning pins outstanding from said flat face outside the bushing edge; a series of cutters, each having a flat end surface, a fiat radial surface, an internal cylindrical surface and an external beveled surface; and a clamping nut adapted to be tightened on said body having an internal beveled surface to engage the beveled surface on each cutter; the said clamping nut when tightened holding the flat end surfaces of the cutters against the flat face of the body, a radial surface of each cutter against a positioning pin, and the internal cylindrical surfaces of the cutters against the cylindrical edge of the bushing.

7. A thread cutting die comprising a body having a fiat faced end; a centra1 hub having an external cylindrical surface outstanding from said fiat faced end; a series of cutters each having a flat faced flanged end, an internal cylindrically curved surface and an external cylindrically curved surface terminating in a beveled portion at its inner flanged end; a clamping element associated with said body and having an internal beveled annular shoulder engaging the external beveled surface of each cutter, whereby the flat faced ends of the cutters'al'e clamped against the fiat faced end of the body and the internal curved surfaces of the cutters are clampedagainst the external cylindrical surface 2.33am: a 3

outstanding from said fiat faced end of the body.

clamping element associated with said body and having an internal beveled annular shoulder enaging the external beveled surface of each cutter, whereby the fiat faced ends or the cutters are clamped against the flat faced end of the body and the internal curved surfaces of the cutters are clamped against the head-of the bushing.

, MAURICE L. BURT. 

